The present invention relates to a system and method for measuring the grip performance of a vehicle, such as a passenger car, a racing car, a motorcycle, or the like, through relation to a lumped-sum parameter derived from force and linear and/or angular displacement measurements taken from selected elements forming the suspension of the vehicle. In deriving this parameter as representative of the time dependent grip forces developed between the tire of the car and the surface of the road, the present invention establishes a criteria for comparing and optimizing the ultimate effects of mechanical and aerodynamic changes or adjustments made in the car or to its components, and additionally allows for the determination of the absolute values of the forces acting upon each wheel of the car and for the comparison of road surface grip.
The measurement of what may be termed as the "performance" of a car is a problem which has long perplexed both the car engineer and the tire designer alike. Broadly, the overall performance of a car may be based on any or all of its front and rear braking, acceleration, and cornering response. Improvements in performance may be effected by improving the fixed mechanical and aerodynamic design parameters of the car, and/or by dynamically compensating for inadequacies in such design by using computationally controlled corrective systems such as and-locking brakes, traction control, and active ride height systems. Thus far, however, the performance analysis of the design or corrective system has lagged behind the design itself for want of analytical data and criteria upon which an improvement in performance might be determined. Complicating the matter is that the individual responses which combine to give a car its overall performance each depend not on one parameter, but ultimately upon a complex, three-dimensional interaction between innumerable variables such as: the design and construction of the tires; the design of the mechanical systems, chassis, suspension, and frame including mass distribution and aerodynamic effects; and the road and driving conditions including the road surface and ambient temperature. The interactive effects of each of these variables must be considered by any system which would be capable of measuring car performance.
Heretofore, attempts at measuring and managing car performance have focused either on subjective "seat of the pants" and trial-and-error techniques, or more recently on complex computational modeling directed to simulate at least some of the interactive variables affecting the braking, acceleration, and cornering responses of the car. The complexities of the interactions between those variables, however, have proved unmanageable at best to even approximate car performance. For example, even with the mechanical systems and aerodynamic components of a given car left unchanged, such transient phenomena as variations in road or track and ambient conditions appreciably affect car performance to a degree, at least in auto racing, which can be the measure between winning and losing. As illustrative of the complexities involved in computationally modeling car performance, Table I lists only a few of the elements which must be considered as affecting the grip, balance, or drag of the car.
TABLE I ______________________________________ System or Condition Variable or Measurement ______________________________________ Tires Instantaneous camber as affected by camber change characteristics, static settings, car roll, car structural integrity, Ackerman steering geometry, steering angle, and tire load Instantaneous toe in or out as affected by dynamic toe change, static toe setting, car structural integrity, and tire load Instantaneous tire pressure Tire mileage or wear as affecting acceleration, lateral cornering, and steady-state running. Tire temperature and temperature distribution Mechanical Weight distribution and front and rear sprung and unsprung weight as affected by fuel load and component wear Front and rear track width Height of sprung and unsprung center of mass Torsional rigidity of car front to rear at center line as affected by temperature and instantaneous structural stresses Aerodynamic Front wing mainplane proximity to ground and (Racing) angle Left and right flap angles and front wing skirt positions Front and rear brake duct type Front and rear wing, and under wing gurney lip configuration Rear wing type and angle Engine RPM as affecting underwing exit because of exhaust gases Radiator type and inlet and exit opening detail Engine inlet detail Proximity of rear wheel to bodywork Roll hoop and windscreen type, height, and detail Setup Front and rear springs, suspension, and anti roll Adjustments bar wheel rates Front and rear shock absorbers valving bump and release low and high speed rates Front left and right side caster Instantaneous front and rear ride height and roll center position Dynamic car cross weight Rear tire staggered diameters Ambient Track or road temperature and surface type and Conditions condition Air temperature ______________________________________
Nowhere is the gap between performance design and performance analysis as evident as in the sport of auto racing. In most classes of auto racing, and especially with "Indy" cars, there exists an anomaly in that car specifications are intentionally made restrictive to force a competitive similarity in approach to both car design and performance. Unfortunately, at least from the standpoint of the engineer or designer, the upper echelons of competitive auto racing, including both "Indy" or CART and Formula 1, have or will have banned the use of closed-loop systems for controlling the corrective systems of the car. The need, therefore, to optimize the performance of the car during its design and pre-race tuning or setup stages now has become even more critical to achieving consistently fast lap times. Indeed, there has been seen performance fluctuations as between teams running the same make of car, and even as within the same team on different days or on different tracks.
Currently the braking, acceleration, and cornering performance of race cars are determined at the track in terms of corner speeds and split times, dynamic ride height change, longitudinal and lateral accelerations, shock displacements, and engine and tire temperatures and pressures. None of this data, however, definitively provides a quantitates measurement of the determinative factor of car performance, that of the grip force. Accordingly, it is ultimately the driver who now is called upon to subjectively judge the relative, performance of the car on any one day and in response to what may be the cumulative effects of a plethora of design changes or adjustments, or simply a change in track or ambient conditions. With different drivers, however, come different "seat of the pants" opinions as to the level of car performance. Even as to the same driver, his or her experience level and present state of mind affects perceptions and precludes there being any comparative standard upon which the engineer or designer might objectively base performance.
In view of the foregoing, it is apparent that there has existed and remains a need in both the sport of auto racing and in the passenger car industry for a means to optimize, in some objective and predictable manner, all the setup and design variables which ultimately interact to determine the overall performance of the car. Preferably, such means would provide some criteria for objectively comparing and endorsing of the incremental effects on overall performance of changes, improvement, or adjustments made to the mechanical or aerodynamic packages of the car. The preferred means also would consider or be unaffected by such transient phenomena as changes in ambient conditions or road surface type or condition, and additionally would provide a capability for determining the absolute values of the forces acting upon each wheel of the car. Such means would be welcomed by: the design engineer in analytically measuring and comparing the performance of various tire, suspension, mechanical, aerodynamic, and engine designs; by the track or race engineer in tuning and optimizing the setup parameters of the racing car prior to a run; and by the driver in allowing for the design of various closed-loop control, warning, or safety systems which, for example, might be linked to engine speed for enabling safe cornering operation.